Arsenal lost for the first time since the opening day of the Premier League campaign, as last season's beaten finalists Borussia Dortmund beat the English side 2-1 in London.

Olivier Giroud cancelled out Henrikh Mkhitaryan's opener before Polish striker Robert Lewandowski scored the winner, although he was fortunate to be on the pitch having elbowed Laurent Koscielny earlier in the second half.

After three rounds of games, Dortmund tops the Group F table on goal difference from Arsenal, while Napoli also joined the clubs on six points after disposing of Marseille 2-1 in France.

Arsenal's English rivals Chelsea enjoyed better fortune against German opposition as a double from Torres - taking his tally to 39 for the London club - and one from Eden Hazard saw them win 3-0, inflicting a first defeat of the campaign on Schalke 04 in Group E.

Both Chelsea and Schalke are on six points while Basel, surprise winners over Chelsea in the first match, are on four points after being held 1-1 by previously pointless Steaua Bucharest in Romania.

Steaua scored a late equaliser but have now gone a record 12 home matches without a win in the competition.

The night's highest profile match ended in a 1-1 draw in Italy between AC Milan and Barcelona as Argentina's four-time world player of the year Lionel Messi scored a fine equaliser to show he had put behind him the thigh injury that kept him out for three weeks.

That goal cancelled out Robinho's opener but, despite dominating the second half, Barcelona was unable to break down an obdurate Milan defence and dropped the team's first points of the campaign.

Barcelona leads Group H with a two-point advantage over Milan while Celtic kept hopes alive of reaching the last 16 for the second successive season with a 2-1 win at home to Ajax.

The result sees the Scottish champions move onto three points at the halfway stage.

Atletico Madrid had no trouble in making it three wins from three as the team rebounded from a first league defeat of the season at the weekend to trounce Austria Vienna 3-0 away in Group G.

A double from Brazil-born striker Diego Costa - one a magnificent solo run from the halfway line - on his return from a European ban was the foundation of Atletico's victory.

The Spanish side can wrap up a place in the knockout stages should it beat the same opponents in early November as it leads Zenit St Petersburg by five points and third-placed Porto by six.

Zenit ran out 1-0 winners over a Porto side that played with just 10 men from the sixth minute when Hector Herrera was sent off.

Aleksandr Kerzhakov struck the winner shortly before full-time in Oporto.